A display device for displaying an arbitrary image is known, in which a plurality of gas discharge tubes each comprising a small glass tube having an internal diameter of about 0.5–5 mm are arranged in an array form.
In the small glass tube used as the gas discharge tube for the display device, a phosphor layer for converting ultraviolet light generated by discharge to visible light is formed. As a method for forming the phosphor layer in the small glass tube, a method of forming the phosphor layer directly on an inner wall of the small glass tube is well known. There is also a method of forming the phosphor layer on a supporting member separated from the small glass tube and then inserting it in the small glass tube as described in Japanese Patent Application No. 2001-276941 which is also an application by applicant of the present application.
When compared to the method of forming the phosphor layer directly on the inner wall of the small glass tube, the method of forming the phosphor layer in the small glass tube by inserting the supporting member having the phosphor layer formed thereon (hereafter referred to as “phosphor layer supporting member”) into the small glass tube has an advantage that a uniform phosphor film can be formed easier. On the other hand, fabrication of the supporting member is not easy because the supporting member needs to be a structure which is slimmer than the small glass tube and almost the same as the small glass tube in length, and needs to have an almost the same expansion coefficient as that of the small glass tube.
For the above reasons, there has been a demand for a method for easily and efficiently fabricating the supporting member for forming the phosphor layer thereon, which is insertable in the small glass tube to be used as the gas discharge tube.
In view of the above circumstances, the present invention is directed to a method for efficiently forming a phosphor layer in a gas discharge tube by drawing a base material to fabricate a supporting member which is insertable in a small glass tube to be used as the gas discharge tube, forming a phosphor layer on the supporting member, and then inserting and placing the supporting member in the small glass tube.